1. Field of the Invention
The invention relates to a matrix printer having a carriage which is movable to and fro along a paper guide and on which there is arranged a printing head having different printing positions for which purpose it is relatively pivotable with respect to the carriage about an axis which extends perpendicularly to the line direction and also perpendicularly to the surface of the paper to be printed, the relative pivoting motion of the printing head with respect to the carriage being realized by means of a magnetically activatable position changer which exerts a torque on the printing head.
2. Description of the Prior Art
In a known matrix printer of the kind set forth (U.S. Pat. No. 4,031,992) the position changer consists of an arm which is connected to the printing head near one end and which comprises on its other end a knob which is movable by means of an electromagnetic drive. The electromagnetic drive may be indirect by means of an adjustable toothed segment which does not move to and fro with the carriage and which engages the knob near the reversing point of the carriage, or direct by connection of the armature of an electromagnet mounted on the carriage to the knob. It is a drawback of the indirect drive that via the arm a substantial impact force is exerted on the printing hand by the toothed segment when the toothed segment is approached at a comparatively high speed by the knob. If the toothed segment is approached at a comparatively low speed in order to prevent an excessive impact force, the printing speed will be adversely affected. The direct drive has the drawback that in the case of a comparatively fast printing head adjustment, the impact forces on the vulnerable armature of the electromagnet have to be taken into account. A comparatively slow printing head adjustment adversely affects the printing speed again. The fixed connection between the armature and the printing head renders the construction susceptible to dimensional deviations of the parts.
It is to be noted that U.S. Pat. No. 4,010,835 describes a matrix printing head where one part of a two-part printing head is displaced with respect to another part of the printing head by means of an electromagnet which is mounted on the carriage which is movable to and fro. Thus, this printing head is not a printing head which is pivotable in its entirety. The two-part printing head is comparatively expensive, because both parts have to be guided and supported. U.S. Pat. No. 4,010,835 also describes a printing head which is pivotable in its entirety. It is not disclosed how the pivoting motion is realized.